A conventional apparatus for controlling a low DC-DC converter (LDC) operates a variable voltage controller to determine a command voltage according to the purposes of fuel efficiency, load performance, and auxiliary battery protection, and operates a controller for compensating for voltage drop at an output terminal of the LDC to regulate the command voltage determined by the variable voltage controller to correspond to a terminal voltage of an auxiliary battery.
The variable voltage controller and the controller for compensating for voltage drop at the output terminal of the LDC may operate at all times in a normal operating state of the LDC. However, the controllers may stop when limiting a charging current for preventing the overcharging of the auxiliary battery, and a controller for limiting a charging current of the auxiliary battery may only operate to determine a command voltage of the LDC and limit the charging current.
When limiting an output current of the LDC, the variable voltage controller, the controller for compensating for voltage drop at the output terminal of the LDC, and the controller for limiting the charging current of the auxiliary battery may stop operating, and a controller for limiting the output current of the LDC may only operate to determine the command voltage of the LDC. When the operations of the controllers (logics) are stopped in particular states as described above, LDC voltage is instantaneously changed in state transitions, which may cause an increase in user inconvenience or discomfort due to instantaneous overcurrent or variations in electrical load performance.
Consequently, in the conventional apparatus for controlling an LDC, the variable voltage controller and the controller for compensating for voltage drop at the output terminal of the LDC may operate at all times in the normal operating state of the LDC, but stop operating when the controller for limiting the charging current of the auxiliary battery operates. When the controller for limiting the output current of the LDC operates, the controller for limiting the charging current of the auxiliary battery as well as the variable voltage controller and the controller for compensating for voltage drop at the output terminal of the LDC stop operating. Thus, the LDC voltage is instantaneously changed in the state transitions of respective controllers, leading to instantaneous overcurrent and electrical load performance degradation.